With the Rio Olympics already criticized over poor housing for athletes, terror threats and Brazil's political crisis, a new problem has emerged sluggish tickets sales.

Masses of empty seats at events have been blamed on the Zika virus, rising crime and other worries. And the problem is strikingly evident, with TV pictures revealing the extent of it, even at popular events.

For less-popular events ― such as rugby, hockey and equestrian ― ticket sales are so low that the Rio Olympic committee gave away about 280,000 to underprivileged children to fill in the seats.

The problem has become so deep that Jamaica's Usain Bolt, the world record holder in the men's 100m and 200m sprints, posted a video encouraging fans to buy tickets to come and cheer for him.

The gaps in the stands are being blamed on factors ranging from inaccessible venues and lengthy security checks, to fears of Zika and Brazil's recession.